This invention relates generally to systems for retrieving large volumes of digital data on demand and, more particularly to solid state mass storage devices for storing and retrieving data for interactive applications, such as video-on-demand applications. There is a growing need for solid state mass storage devices to support highly interactive multimedia applications, such as video on demand for cable television operation, interactive learning for schools and businesses, and data service for business and financial use. Different interactive application types require servers having different characteristics to retrieve and generate the appropriate data streams. For example, small servers can be used to handle business or educational applications with up to a few hundred users requesting data. Large, centrally located servers with large storage capacities may be needed to handle the needs of systems serving thousands of servers simultaneously.
All data servers have in common a hierarchy of memory storage media, and an output interface to a standard information delivery system, sometimes referred to as an information highway. Applications having a small number of users and requiring little interaction between the user and the information can be served with inexpensive storage media, such as optical or magnetic disks. As the number of users increases, the need for higher performance media also increases. In general, the servers should employ storage media optimized for each particular use and for user requirements. Thus the media may include digital tape, optical disks, magnetic disks, redundant arrays of inexpensive disks (RAID), and solid state memories. The present invention pertains specifically to data servers using solid state memory as the storage medium.
Prior to this invention, data storage systems available or proposed for highly interactive multimedia applications, such as video on demand, interactive learning and data services, have employed adaptations of existing computer technology, including magnetic disk drives, redundant arrays of inexpensive disks (RAID), optical disks and magnetic tape drives. Typically, servers prior to the present invention have a capability of providing one to two hundred streams of data to separate users. A desirable goal is to generate as many as two thousand data streams simultaneously.
More specifically, there is a need for a solid state memory to provide high output speed, which is needed to service large numbers of users simultaneously; rapid access, for highly interactive operation; the ability to output in a standard data transfer format without the need for an external processor; the ability to receive inputs from other storage devices over standard high speed interconnects; and a modular structure to facilitate expansion as needed. The present invention satisfies and exceeds these requirements.